Film grain forms in motion picture images during the process of development. Film grain is clearly noticeable in high definition (HD) images and becomes a distinctive cinema trait that should be preserved through the whole image processing and delivery chain. Nevertheless, film grain preservation is a challenge for current encoders since compression gains related to temporal prediction cannot be exploited. Due to the random nature of the grain, visually lossless encoding is only achieved at very high bit-rates. Lossy encoders tend to suppress the film grain when filtering the high frequencies typically associated with noise and fine textures.
Film Grain Management (FGM, also referred to herein as Film Grain Technology, or FGT) has been presented as a new way of encoding the grain in motion picture film by means of a parameterized model to be transmitted as parallel information. To support FGT, the Fidelity Range Extension (FRExt) Amendment to the ITU-T Rec. H.264 | ISO/IEC 14496-10 | MPEG-4 AVC | Joint Video Team (JVT) standard (hereinafter the “H.264 standard”) has defined a film grain characteristics Supplemental Enhancement Information (SEI) message. The SEI message describes the film grain characteristics regarding attributes such as size and intensity, and allows a video decoder to simulate the film grain look onto the decoded picture. The H.264 standard specifies which parameters are present in the film grain characteristics SEI message, how to interpret the parameters, and the syntax for encoding the SEI message in binary format. However, the H.264 standard does not specify the exact procedure to simulate film grain upon reception of the film grain characteristics SEI message. It is to be appreciated that FGT can be used jointly with any other video coding method since it utilizes parallel information, transmitted from an encoder, that does not affect the decoding process.
In FGT, the encoder models the film grain of the video sequence and the decoder simulates the film grain according to the received information. The encoder can use FGT to enhance the quality of the compressed video when there is difficulty retaining the film grain. Additionally, the encoder has the option of removing or attenuating the grain prior to encoding in order to reduce the bit-rate.
Film grain simulation aims at synthesizing film grain samples that simulate the look of original film content. Unlike film grain modeling, which is entirely performed at the encoder, film grain simulation is performed at the decoder. Film grain simulation is done after decoding the video stream and prior to display. Images with added film grain are not used within the decoding process. Being a post-processing method, synthesis of simulated film grain on the decoded images for the display process is not specified in the H.264 standard. The film grain simulation process includes the decoding of film grain supplemental information, transmitted in a film grain characteristics SEI message as specified by the Fidelity Range Extensions Amendment of the H.264 standard.
Thus, it is to be appreciated that film grain simulation is a relatively new technology used in post-production to simulate film grain on computer-generated material, as well as during restoration of old film stocks. For these types of applications, there exists commercial software in the market like Cineon®, from Eastman Kodak Co, Rochester, N.Y., and Grain Surgery™, from Visual Infinity. These tools generally operate based on user interaction and are complex to implement, which makes them unsuitable for real-time video coding applications. Furthermore, none of these tools has the capability to interpret a film grain characteristics SEI message as specified by the H.264 standard.
Based on the aforementioned Supplemental Enhancement Information (SEI) message, several prior art approaches have been developed relating to specifications for simulating film grain. These prior art approaches target high quality applications and provide large flexibility in the simulation of different film grain patterns on both luma and chroma color components with a small increase in computational cost. However, during trick mode play, like fast forward or jumps, these prior art approaches consider several special cases that undesirably add additional complexity and result in inconsistent film grain simulation.
Accordingly, it would be desirable and highly advantageous to have methods and apparatus for bit-accurate film grain simulation for normal play and trick mode for standard definition (SD) and high definition (HD) DVD systems that is more efficient to implement than related prior art approaches while maintaining a consistent film grain simulation unlike the related prior art approaches.